Tetrazolium violet staining of naturally and artificially moulded sorghum (Sorghum bicolor (L.) Moench) caryopses

Sorghum grain mould (GM) is a yield-limiting disease characterized by damage to caryopsis embryo tissues. Caryopses were obtained from naturally weathered (n.w.) panicles and panicles inoculated with Fusarium thapsinum (FT) and Curvularia lunata (CL) at anthesis. Caryopses were assayed for tetrazolium violet (TZ) viability, embryo damage, germination, and pathogen isolation. In n.w. and artificially inoculated (a.i.) caryopses, Tx430 (GM-susceptible) showed low whole embryo TZ viability, whereas Sureno and Tx2911 (GM-resistant) showed higher values. Tx430 had the greatest levels of non-staining scutellum, coleoptile, plumule, radicle tissues, non-staining tissues and damaged embryos under both inoculation regimes. In n.w. grain, TZ staining overestimated germination for some genotypes (especially Tx430), whereas TZ staining underestimated germination in most a.i. material. Correlations between TZ viability and germination were positive and significant for n.w. and a.i. caryopses. FT and F. proliferatum (FP) were the most commonly isolated fungi from n.w. grain. Correlations between yellow-pigmented-FT, FP, and CL incidence from sorghum caryopses and TZ viability were negative and significant. This study showed that TZ viability differs in a genotype- and pathogen-dependent manner. Therefore, this approach will have utility in screening sorghum germplasm for grain mould resistance at the whole embryo and tissue level.